The present invention relates generally to self-propelled sprinkler irrigation apparatus and more particularly to the type utilized for irrigating large sections of land. The invention relates specifically to an electronic control system for maintaining the linear alignment of the sprinkler irrigation apparatus and for shutting the apparatus down if the misalignment becomes too severe as to be uncorrectable by the control system.
The type of self-propelled sprinkler irrigation apparatus shown in the drawings is a type known in the art as a pivotal irrigation system consisting of a plurality of end-coupled adjacent irrigation pipes, all the sections extending radially outward from a pivot center for distances up to a quarter of a mile. Each of the sections is supported by a tower and each tower is driven by some type of drive means, causing the irrigation system to rotate around the center pivot point. As is apparent, the outer tower must travel farther than the tower adjacent to it, and so forth, moving inward towards the pivot of the irrigation apparatus. Typically the drive means on the separate towers consist of electric motors which are either on or off to keep said system moving in a predetermined direction.
It is necessary that the system be kept in linear alignment within acceptable limits, so that the irrigation pipe and its couplings are not damaged and so that the system will continue to rotate in an acceptable manner. In the past, this has been accomplished through alignment control systems consisting of photoelectric devices, microswitches, or permanent magnets and magnetic reed switches utilized as sensors to sense the linear misalignment of the system generating an electrical signal which is then utilized to drive the system back into linear alignment.
Photoelectric systems and microswitch systems tend to be expensive and/or unreliable. The known systems utilizing a permanent magnet and a reed switch require that the permanent magnet and the reed switch be selected so as to be compatible with each other and this makes it difficult to design a system whereby one is assured that when the permanent magnet is within a predetermined distance from the reed switch that the reed switch will close. That is to say, it is difficult, if not impossible, to design a system whereby sensing means utilized to sense the linear misalignment of the system is of a very exact nature. Alignment and adjustment of such known systems is tedious and difficult.